JP7038956B2 - Negative electrode active material with high output characteristics and lithium secondary battery containing it - Google Patents

Description

The present invention relates to a negative electrode active material having high output characteristics and a lithium secondary battery containing the same.

This application claims priority based on Korean Patent Application No. 10-2017-0035600 filed on March 21, 2017, and all the contents disclosed in the specification and drawings of the relevant application are incorporated in this application. To.

As fossil fuel depletion raises the price of energy sources and raises concerns about environmental pollution, environmentally friendly alternative energy sources have become an essential factor for future life.

With the expansion of application fields to the energy of mobile phones, camcoders and laptop computers, and even electric vehicles, efforts for research and development of electrochemical elements are becoming more and more concrete.

Electrochemical devices are the field that has received the most attention from this aspect, and the development of secondary batteries that can be charged and discharged freely is of particular interest. In recent years, in the development of such batteries, research and development related to the design of new electrodes and batteries have been carried out in order to improve the capacity density and specific energy.

Particularly in recent years, in the case of lithium secondary batteries, the use as a power source for electric vehicles (EV), hybrid electric vehicles (HEV), micro-hybrid vehicles (μ-HEV), etc. has been realized, and power assistance through grid formation has been realized. The range of use is expanding as a power source and other applications.

The micro-hybrid vehicle partially uses a secondary battery, and the development of the 12V dual or 48V secondary battery used therein is proceeding in the direction of demanding higher output performance.

On the other hand, lithium-titanium oxide is expected to be applied as a negative electrode material for high output because the efficiency of the initial charge and discharge cycle is close to 100%, the operating voltage is high, and the surface film of the negative electrode is not formed by the electrolyte decomposition reaction. ing.

Therefore, in order to realize the high-speed charge / discharge characteristics of 20C or more, it is essential to apply lithium titanium oxide, but there is a problem that the corresponding output cannot be satisfied with the conventionally used lithium titanium oxide.

Therefore, there is still a need to develop a lithium titanium oxide negative electrode material that can be applied to the field of hybrid automobiles that require high output characteristics.

Therefore, an object to be solved by the present invention is to provide a negative electrode active material that can be used in a battery having high output characteristics and whose manufacturing process is easy.
Another problem to be solved by the present invention is to provide a lithium secondary battery including the negative electrode active material.

In order to solve the above problems, according to one aspect of the present invention, the negative electrode active material of the following embodiment is provided.

The first embodiment is a negative electrode active material containing lithium titanium oxide particles, wherein the lithium titanium oxide particles have an average particle size (D50) of 0.5 μm to 9 μm and 3 m ² / g to 7 m ² / g. It relates to a negative electrode active material having a specific surface area and a pellet density of 1.7 g / cc or more under a pressure of 64 MPa, and the lithium titanium oxide is represented by the following chemical formula 1.

[Chemical 1]
Li _{x Ty Oz M w}
(In the formula, M is one or a mixture of two or more selected from the group consisting of Zr, B, Sn, S, Be, Ge and Zn, 0.5 ≦ x ≦ 5, 1 ≦ y ≦ 5. , 2 ≦ z ≦ 12, 0 ≦ w <0.1)

The second embodiment relates to one or more negative electrode active materials selected from the group in which the lithium titanium oxide particles consist of primary particles and secondary particles formed from the primary particles in the first embodiment.

The third embodiment is a negative electrode active material in which the primary particles have an average particle size (D50) of 0.2 μm to 1.2 μm and a specific surface area of 5 m ² / g to 7 m ² / g in the second embodiment. Regarding.

The fourth embodiment relates to a negative electrode active material in which the primary particles have a pellet density of 1.7 g / cc to 1.82 g / cc under a pressure of 64 MPa in the second embodiment or the third embodiment.

A fifth embodiment relates to a negative electrode active material in which the secondary particles have an average particle size (D50) of 2 μm to 9 μm and a specific surface area of 3 m ² / g to 4.9 m ² / g in the second embodiment.

The sixth embodiment relates to a negative electrode active material in which the secondary particles have a pellet density of 1.75 g / cc to 1.85 g / cc under a pressure of 64 MPa in the second embodiment or the fifth embodiment.

In the seventh embodiment, in any one of the second embodiment to the sixth embodiment, the lithium titanium oxide particles are a mixture of primary particles and secondary particles, and the primary particles and 2 are used. It relates to a negative electrode active material having a weight ratio of 1: 9 to 4: 6 with subatomic particles.

In the eighth embodiment, in any one of the first embodiment to the seventh embodiment, the lithium titanium oxide is Li _0.8 Ti _2.2 O ₄ , Li _2.67 Ti _1.33 O. 4. One or more selected from the group consisting of ₄ , Li _1.33 Ti _1.67 O ₄ , Li _1.14 Ti _1.71 O ₄ , Li ₄ Ti ₅ O ₁₂ , Li Ti ₂ O ₄ and Li ₂ TiO ₃ . Regarding the negative electrode active material of.

In the ninth embodiment, in any one of the first embodiment to the eighth embodiment, the negative electrode active material is a carbonaceous material; Si, Sn, Li, Zn, Mg, Cd, Ce, Ni or Fe. Metals (Me); alloys of the metals (Me); oxides of the metals (Me) (MeOx); and composites of the metals (Me) and carbon. The present invention relates to a negative electrode active material further comprising any one active material or a mixture of two or more of them.

In order to solve the above problems, according to another aspect of the present invention, a lithium secondary battery according to the following embodiment is provided.

The tenth embodiment includes a positive electrode containing a positive electrode active material, a negative electrode containing a negative electrode active material, a separator interposed between the positive electrode and the negative electrode, and an electrolytic solution, and the negative electrode active material is the first embodiment. The present invention relates to a lithium secondary battery which is a negative electrode active material of any one of the ninth embodiment.

According to one embodiment of the present invention, by using a negative electrode active material obtained by controlling the range of average particle size (D50), specific surface area (BET), and pellet density of particles, the capacity at a high rate is used. It can be applied to automobile batteries that require high output, such as microhybrid batteries, by improving the maintenance rate and securing the initial capacity.

Hereinafter, the present invention will be described in detail. Prior to this, the terms and words used herein and in the scope of the claims should not be construed in a general or lexical sense only, and the inventor himself should explain the invention in the best possible way. It must be interpreted in the meaning and concept corresponding to the technical idea of the present invention in accordance with the principle that the concept of terms can be properly defined. Therefore, the examples and configurations described herein are merely one of the most desirable embodiments of the invention and do not represent all of the technical ideas of the invention and are therefore at the time of this application. It must be understood that there can be a variety of equivalents and variants that can be substituted for.

The negative electrode active material according to one aspect of the present invention is a negative electrode active material containing lithium titanium oxide particles, wherein the lithium titanium oxide particles have an average particle size (D50) of 0.5 μm to 9 μm, and 3 m ² / g to. The lithium titanium oxide has a specific surface area of 7 m ² / g and a pellet density of 1.7 g / cc or more under a pressure of 64 MPa, and the lithium titanium oxide is a negative electrode active material represented by the following chemical formula 1.

[Chemical 1]
Li _{x Ty Oz M w}
(In the formula, M is one or a mixture of two or more selected from the group consisting of Zr, B, Sn, S, Be, Ge and Zn, 0.5 ≦ x ≦ 5, 1 ≦ y ≦ 5. , 2 ≦ z ≦ 12, 0 ≦ w <0.1)

Further, the lithium titanium oxide may have one or more crystal structures of a spinel type, a perovskite type, and an orthorhombic type, but is not limited thereto.

The lithium titanium oxide is, for example, Li _0.8 Ti _2.2 O ₄ , Li _2.67 Ti _1.33 O ₄ , Li _1.33 Ti _1.67 O ₄ , Li _1.14 Ti _1.71 . It can be O ₄ , Li ₄ Ti ₅ O ₁₂ , LiTi ₂ O ₄ and Li ₂ TiO ₃ , and more specifically, Li ₄ Ti ₅ O ₁₂ and Li, which have an excellent spinel structure with little change in crystal structure during charging and discharging. It can be _1.33 Ti _1.67 O ₄ or LiTi ₂ O ₄ . However, it is not limited to these.

According to one embodiment of the present invention, the lithium titanium oxide (LTO) is in the form of lithium titanium oxide primary particles, or in the form of secondary particles formed by agglomeration of a plurality of primary particles, or 1 It can be in the form of a mixture of subatomic particles and secondary particles.

Further, according to one embodiment of the present invention, the lithium titanium oxide may contain a small amount of unaggregated free lithium titanium oxide primary particles in addition to the lithium titanium oxide secondary particles, but substantially. Can consist of secondary particles.

According to one embodiment of the present invention, the lithium titanium oxide used as the negative electrode active material is, specifically, the lithium titanium oxide in the secondary particle form is 100% by weight of the lithium titanium oxide contained in the negative electrode. On the other hand, it may be 60% by weight or more, 70% by weight or more, 80% by weight or more, 90% by weight or more, 95% by weight or more, or 99% by weight or more.

According to one embodiment of the present invention, when the lithium titanium oxide (LTO) is in the form of a mixture of lithium titanium oxide primary particles and secondary particles, the weight ratio of the primary particles to the secondary particles. Can be 1: 9 to 4: 6, specifically 1: 9 to 3: 7. When the range of such a weight ratio is satisfied, it can be applied to a high output battery according to a predetermined pellet density.

In the present invention, the lithium titanium oxide particles have an average particle size of 0.5 μm to 9 μm (volume-based average particle size, D50), specifically 2 μm to 8 μm, and more specifically 3.5 μm to 7.5 μm. Can have an average particle size.

Specifically, when the lithium titanium oxide particles are primary particles, the D50 of the primary particles may be 0.2 μm to 1.2 μm, more specifically 0.4 μm to 0.7 μm. When the lithium titanium oxide particles are secondary particles, the D50 of the secondary particles may be 2 μm to 9 μm, more specifically 3.5 μm to 8.2 μm. Here, D50, which is the volume-based average particle size, means the particle size of the particles corresponding to 50% of the total volume when the particle size is measured by the particle size analyzer and the volume is accumulated from the small particles.

The primary particles and the secondary particles can independently have a spherical or similar spherical shape, and the similar spherical shape has a three-dimensional volume including an elliptical shape, and has a morphology. Includes particles of all forms, including non-identifiable irregular shapes.

Further, in one embodiment of the present invention, the negative electrode active material layer has a porous structure in which a large number of pores are present, and such a porous structure depends on, for example, the shape of various lithium titanium oxide particles as described later. It can result from one or more of the features.

The lithium-titanium oxide secondary particles have a porous structure in which a large number of pores are formed on the surface of the secondary particles and inside the main body by a large number of pores formed between the aggregated primary particles. Further, the lithium titanium oxide primary particles may have a porous structure in which a large number of primary pores are formed on the surface and the particle body inside the particles. The large number of the pores can be interconnected with one or more adjacent other pores to function as a passage for the electrolyte. Therefore, a large number of pores formed inside the particles and interconnected serve as a passage for the electrolytic solution.

In the present invention, the lithium titanium oxide particles have a specific surface area of 3 m ² / g to 7 m ² / g, specifically 3.5 m ² / g to 6.5 m ² / g, more specifically 4 m ² / g. It may have a specific surface area of ~ 6.3 m ² / g.

If the specific surface area of the lithium titanium oxide particles satisfies such a range, high output with excellent rate characteristics can be ensured.

Specifically, when the lithium titanium oxide particles are primary particles, the specific surface area of the primary particles is 5 m ² / g to 7 m ² / g, specifically 6 m ² / g to 6.5 m ² / g. obtain. When the lithium titanium oxide particles are secondary particles, the specific surface area of the secondary particles is 3 m ² / g to 4.9 m ² / g, specifically 3.5 m ² / g to 4.8 m ² /. Can be g. Here, the specific surface area was measured using a BET specific surface area analyzer (Brunauer Emmet Teller, BET).

The pellet density (rolling density) is a comparison of how much the negative electrode active material can be rolled when it is rolled. The higher the rolling density, the higher the energy density of the cell, and the lower the rolling density, the higher the particle strength and the lower the content of small particles (primary particles).

The rolling density of the negative electrode active material can be measured using, for example, a powder resistance measuring machine MCP-PD51 manufactured by Mitsubishi Chemical Corporation. In the case of the powder resistance measuring machine, a certain amount of negative electrode active material particles are put into a cylinder type load cell and continuous force is applied to measure the density measured while the particles are pressed. The higher the particle strength, the lower the rolling density because it is pushed a little at the same pressure, and the rolling density can be higher when an appropriate amount of small particle size lithium-titanium oxide particles are present.

In the present invention, the lithium titanium oxide particles have a pellet density of 1.7 g / cc or more under a pressure of 64 MPa, 1.7 g / cc to 1.85 g / cc under a pressure of 64 MPa, and more particularly 1 It can have a pellet density of .74 g / cc to 1.82 g / cc.

Specifically, when the lithium titanium oxide particles are primary particles, the pellet density of the primary particles is 1.7 g / cc to 1.82 g / cc under a pressure of 64 MPa, specifically 1.72 g / cc to. It can be 1.78 g / cc. When the lithium titanium oxide particles are secondary particles, the pellet density of the secondary particles is 1.75 g / cc to 1.85 g / cc, specifically 1.76 g / cc to 1, under a pressure of 64 MPa. It can be .82 g / cc.

When the lithium titanium oxide particles are composed of only primary particles, if the pellet density is 1.7 g / cc or more, the phenomenon that the current collector like Al foil is broken does not occur, but it is composed of secondary particles. If this is the case, the problem of tearing of the current collector cannot be prevented unless the pellet density is 1.75 g / cc or more. When the lithium titanium oxide particles are composed of only primary particles, the pressure is not transmitted to the current collector even if a strong pressure is applied, but when there are large particles (secondary particles), the pressure is applied. This is because the pressure is transmitted to the current collector.

Considering the number of particles, when the lithium titanium oxide particles are composed of only primary particles, the number of primary particles is larger than when they are composed of secondary particles, so that a relatively weak pressure is applied to Al foil. Can be transmitted to a current collector such as. However, when the lithium titanium oxide particles are composed of secondary particles, the number of the lithium titanium oxide particles is smaller than that of the case where the lithium titanium oxide particles are composed of only primary particles, so that the pressure transmitted to one particle is larger and the current collector is collected. The impact applied to can be greater. Therefore, when the lithium titanium oxide particles are composed of secondary particles, they must be sufficiently crimped at the time of electrode production, and at this time, more sufficiently crimped (or more sufficiently pressed) is the same pressure. It means that the condition must receive less force, i.e. the pellet density value must be higher.

Pore formed between two contacted particles by contacting the lithium titanium oxide secondary particles with other secondary particles or with primary particles contained in adjacent other secondary particles. Can affect the porosity properties of the negative electrode active material layer.

The lithium titanium oxide has a spinel structure and has a three-dimensional Li diffusion path, which is advantageous for rapid charging and realization of high output characteristics. In addition, it has excellent structural stability because it has the property of maintaining the original crystal structure during charging and discharging.

Further, the lithium titanium oxide may have a discharge capacity of 70 to 200 mAh / g, preferably 100 to 170 mAh / g, and more preferably 110 to 160 mAh / g.

According to one embodiment of the present invention, the lithium-titanium oxide particles have a crystal grain size of 100 nm to 200 nm, particularly a crystal grain size of 110 nm to 180 nm, and more particularly a crystal grain size of 120 nm to 180 nm. May have.

When the size of the crystal grains is less than 100 nm, the number of grain boundaries is too large, which is disadvantageous for the insertion of lithium ions, and the charging characteristics of the battery may be deteriorated, while 200 nm is used. If it exceeds, lithium ions are difficult to diffuse inside the crystal, and the resistance may increase, leading to a decrease in output.

The crystal grain size of such lithium titanium oxide particles can be confirmed by using TOPAS, which is a commercial program of Rietveld refinement by X-ray diffraction analysis. As a method for measuring grain size using the TOPAS program, a method usually used in the technical field of the present invention can be applied.

In addition, the amount of lithium carbonate, which is a by-product of the production of the lithium titanium oxide, is 2% by weight or less, 1% by weight or less, 0.5% by weight or less, and 0.1% by weight with respect to 100% by weight of the lithium titanium oxide. % Or less, or 0.05% by weight or less.

The lithium titanium oxide can be produced by a method such as a coprecipitation method, which is a liquid phase synthesis method, a sol-gel method, or a hydrothermal method, but is not limited thereto. do not have. As long as it is possible to produce lithium titanium oxide particles having the characteristics of the present invention, the present invention is not limited to a specific production method.

The method for producing the lithium titanium oxide (LTO) according to an embodiment of the present invention is as follows.

First, a lithium-containing precursor (for example, LiOH) and a titanium-containing precursor (for example, TiO ₂ ) are wet-milled, mixed in a solid phase, and dissolved in water with stirring to produce a slurry. Then, it is spray-dried at a predetermined hot air temperature, fired in an oxygen or air atmosphere and pulverized to obtain a lithium titanium oxide powder.

At this time, when the lithium titanium oxide is produced as primary particles, the particle size can be controlled when the lithium titanium oxide is produced with the smallest particle size by changing the spray drying conditions, and the particles are fired and then pulverized. Further, when the lithium titanium oxide is produced as secondary particles, it can be produced at a target particle size by changing the spray drying conditions, calcined, and then crushed to obtain the particles.

When wet milling the lithium-containing precursor and the titanium-containing precursor, the particle size of TiO ₂ can be controlled by adjusting the milling time and rpm, whereby the specific surface area (BET) of the lithium titanium oxide particles (powder) can also be controlled. Can be changed. As a method for increasing the specific surface area (BET) of the lithium titanium oxide particles (powder), it is conceivable to change the milling conditions (increase in time, increase in rpm), increase the crushing strength, decrease the firing temperature, and so on. Possible methods for lowering the milling conditions include changing the milling conditions, reducing the crushing strength, and increasing the firing temperature.

In one embodiment of the present invention, the loading amount of the negative electrode active material in the negative electrode may be 0.2 mAh / cm ² to 10 mAh / cm ² .

According to one embodiment of the present invention, the negative electrode active material layer can further contain a binder resin and a conductive material. Here, the negative electrode active material layer can contain a negative electrode active material: a conductive material: a binder resin in a weight ratio of 80 to 95: 3 to 13: 2 to 9.

Further, in the negative electrode active material layer, in addition to the lithium titanium oxide, a carbonaceous material such as artificial graphite or natural graphite usually used as a negative electrode active material; Si, Sn, Li, Zn, Mg, Cd, From metals (Me) which are Ce, Ni or Fe; alloys of the metals (Me); oxides (MeOx) of the metals (Me); and composites of the metals (Me) and carbon. Can further comprise any one active material selected from the group or a mixture of two or more of these.

The binder resin includes, without limitation, polyvinylidene fluoride-hexafluoropropylene, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), carboxymethyl cellulose (CMC), polyvinyl alcohol (PVA), polyvinyl butyral (PVB). ), Polyvinylidene fluoride (PVP), styrene butadiene rubber (SBR), polyamideimide, polyimide, etc., or a mixture of two or more thereof can be used, but the present invention is limited thereto. There is no.

The conductive material is not particularly limited as long as it is an electrically conductive material that does not induce chemical changes, and is, for example, natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, super-P black. , Carbon fiber, metal powder such as copper, nickel, aluminum, silver or metal fiber.

In a specific embodiment of the present invention, the negative electrode can be manufactured by the following method.

First, the negative electrode active material, the binder resin and the conductive material are dispersed in an organic solvent such as ethanol (EtOH), acetone, isopropyl alcohol, N-methylpyrrolidone (NMP), propylene glycol (PG) or an appropriate solvent such as water. Negative electrode slurry is produced and crimped into the form of an electrode, the slurry is coated on a metal foil to form an electrode, or the negative electrode composition is pressed with a roller to form a sheet. Is attached to a metal foil to form an electrode, and the result of the electrode form is dried at a temperature of 100 ° C. to 350 ° C. to form a negative electrode. More specifically, an example of forming the negative electrode can be described by crimping the negative electrode slurry with a roll press molding machine. The roll press forming machine aims to improve the electrode density by rolling and control the thickness of the electrodes. It consists of parts. The rolling process is performed while the rolled electrode passes through the roll press, and the electrode is wound again in the rolled state to complete the electrode. At this time, the pressing force of the press can be controlled to 5 to 20 ton / cm ² , and the temperature of the roll can be controlled to 0 to 150 ° C. The slurry that has undergone the press crimping process undergoes a drying process. The drying step can be carried out at a temperature of 100 ° C. to 350 ° C., specifically 150 ° C. to 300 ° C. At this time, if the drying temperature is less than 100 ° C., the solvent is difficult to evaporate, which is not desirable, and if the drying temperature exceeds 350 ° C., the conductive material may be oxidized. The drying step can be performed at the above temperature for about 10 minutes to 6 hours. In such a drying step, the molded negative electrode composition can be dried (solvent evaporation), and at the same time, powder particles can be bound to improve the strength of the negative electrode.

The lithium secondary battery of the present invention is configured to include the above-mentioned negative electrode, a positive electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolytic solution.

The positive electrode can be produced by applying a mixture of a positive electrode active material, a conductive material and a binder on a positive electrode current collector and then drying the positive electrode, and if necessary, the mixture can further contain a filler. .. The positive electrode active material is a compound capable of reversible insertion and desorption of lithium, specifically one or more metals such as cobalt, manganese, nickel or aluminum and lithium. Lithium composite metal oxides including and can be included. More specifically, the lithium composite metal oxide is a lithium-manganese oxide (for example, LiMnO ₂ , LiMn ₂ O ₄ or the like), a lithium-cobalt oxide (for example, LiCoO ₂ or the like), or a lithium-nickel oxide. Oxides (eg, LiNiO ₂ ), lithium-nickel-manganese oxides (eg, LiNi _1-Y Mn _Y O ₂ (here 0 <Y <1), LiMn _2-z Ni _z O ₄ (here) Then, 0 <Z <2), etc.), lithium-nickel-cobalt oxide (for example, LiNi _1-Y1 Co _Y1 O ₂ (here, 0 <Y1 <1), etc.), lithium-manganese-cobalt oxide. (For example, LiCo _1-Y2 Mn _Y2 O ₂ (here, 0 <Y2 <1), LiMn _{2-z1 Coz1} O ₄ (here, 0 <Z1 <2), etc.), Lithium-nickel-manganese- Cobalt oxide (eg, Li (Ni _p Co _q Mn _r1 ) O ₂ (where 0 <p <1, 0 <q <1, 0 <r1 <1, p + q + r1 = 1) or Li (Ni _p1 Co) _q1 Mn _r2 ) O ₄ (where 0 <p1 <2, 0 <q1 <2, 0 <r2 <2, p1 + q1 + r2 = 2), etc.), or lithium-nickel-cobalt-transition metal (M) oxide (where For example, Li (Ni _p2 Co _q2 Mn _r3 M _S2 ) O ₂ (where M is selected from the group consisting of Al, Fe, V, Cr, Ti, Ta, Mg and Mo, p2, q2, r3 and s2. Is the atomic fraction of each independent element, and examples thereof include 0 <p2 <1, 0 <q2 <1, 0 <r3 <1, 0 <s2 <1, p2 + q2 + r3 + s2 = 1), and the like. Any one or more of them can be contained.
Among them, from the viewpoint of improving the capacity characteristics and stability of the battery, the lithium composite metal oxides include LiCoO ₂ , LiMnO ₂ , LiMn ₂ O ₄ , LiNiO ₂ , and lithium nickel manganese cobalt oxide (for example, Li (Ni _{1 / 1)). 3} Mn _1/3 Co _1/3 ) O ₂ , Li (Ni _0.6 Mn _0.2 Co _0.2 ) O ₂ , Li (Ni _0.4 Mn _0.3 Co _0.3 ) O ₂ , Li (Ni _0.5 Mn _0.3 Co _0.2 ) O ₂ , Li (Ni _0.7 Mn _0.15 Co _0.15 ) O ₂ and Li (Ni _0.8 Mn _0.1 Co _0.1 ) O ₂ etc.) or lithium nickel cobalt aluminum oxide (for example, Li (Ni _0.8 Co _0.15 Al _0.05 ) O ₂ etc.) can be used, and in particular, the output characteristic effect after storage due to a voltage increase can be used. In order to further improve the above, the lithium composite metal oxide may contain LiMnO ₂ or LiMn ₂ O ₄ (LMO), which are lithium-manganese-based oxides.

The positive electrode active material can be contained in an amount of 80% by weight to 99% by weight based on the total weight of the solid content in the positive electrode slurry. Non-limiting examples of the positive electrode current collector include aluminum, nickel, or foil manufactured by a combination thereof. For the conductive material and the binder, the above-mentioned description about the negative electrode can be referred to.

The separator is usually in the form of a porous substrate alone having a large number of pores, or a porous coating layer containing a large number of inorganic particles and a binder polymer coated on at least one surface of the porous substrate. Can be in the form of.

The porous substrate can be a porous polymer substrate, and specific examples thereof include a porous polymer film substrate and a porous polymer non-woven substrate.

The porous polymer film base material may be a porous polymer film made of a polyolefin such as polyethylene or polypropylene, and such a polyolefin porous polymer film base material shuts down at a temperature of, for example, 80 to 130 ° C. Fulfill function.

Further, the porous polymer film base material can also be produced by molding it into a film using various polymers such as polyester in addition to polyolefin. Further, the porous polymer film base material can be formed in a structure in which two or more film layers are laminated, and each film layer is a polymer such as the above-mentioned polyolefin or polyester alone or a mixture of two or more thereof. It can also be formed from macromolecules.

In addition to the above-mentioned polyolefin-based materials, the porous polymer film base material and the porous non-woven fabric base material include polyethylene terephthalate, polybutylene terephthalate, polyester, polyacetal, polyamide, polycarbonate, polyimide, and polyether ether ketone. Polyether sulfone, polyphenylene oxide, polyphenylen sulphide, polyethylene naphthalate and the like can be formed from a polymer alone or a mixture thereof. The thickness of the porous substrate is not particularly limited, preferably 1 to 100 μm, more preferably 5 to 50 μm, and the size and degree of pores present in the porous substrate are not particularly limited. It is desirable that it is 0.01 to 50 μm and 10 to 95%, respectively.

In the separator according to one aspect of the present invention, as the binder polymer used for forming the porous coating layer, a polymer usually used for forming the porous coating layer in the art can be used. In particular, polymers with a glass transition temperature ( _Tg ) of -200 to 200 ° C. can be used, which are mechanical such as the flexibility and elasticity of the finally formed porous coating layer. This is because the physical properties can be improved. Such a binder polymer plays a role of a binder that connects and stably fixes the inorganic particles to each other, so that it is possible to prevent deterioration of the mechanical properties of the separator into which the porous coating layer is introduced.

Further, the binder polymer does not necessarily have to have ionic conductivity, but when a polymer having ionic conductivity is used, the performance of the electrochemical element can be further improved. Therefore, the binder polymer having a high dielectric constant can be used as much as possible. In fact, the degree of dissociation of the salt in the electrolytic solution depends on the dielectric constant of the solvent of the electrolytic solution. Therefore, the higher the constant of the dielectric constant of the binder polymer, the more the degree of dissociation of the salt in the electrolyte can be improved. The dielectric constant of such a binder polymer can be in the range of 1.0 to 100 (measurement frequency = 1 kHz), and may be 10 or more in particular.

In addition to the above-mentioned functions, the binder polymer may have a feature of gelling when impregnated with the liquid electrolytic solution and exhibiting a high degree of swelling of the electrolytic solution (degree of swelling). Therefore, the solubility index of the binder polymer, that is, the Hildebrand solubility parameter is in the range of 15 to 45 MPa ^1/2 or 15 to 25 MPa ^1/2 or 30 to 45 MPa ^1/2 . Therefore, a hydrophilic polymer having more polar groups than a hydrophobic polymer such as polyolefin can be more preferably used. This is because when the solubility index is less than 15 MPa ^1/2 or more than 45 MPa ^1/2 , it may be difficult to swell with a normal liquid electrolyte for batteries.

Non-limiting examples of such a binder polymer include polyvinylidene fluoride-hexafluoropropylene, polyvinylidene fluoride-trichloroethylene, polymethylmethacrylate, polybutylacrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinylacetate, and ethylenevinylacetate. Polymers, polyethylene oxide, polyarylate, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cyanoethyl purulan, cyanoethyl polyvinyl alcohol, cyanoethyl cellulose, cyanoethyl sucrose, purulan, carboxymethyl cellulose and the like, but are limited thereto. There is no such thing.

The weight ratio of the inorganic particles to the binder polymer is preferably, for example, 50:50 to 99: 1, and more preferably 70:30 to 95: 5. If the content ratio of the inorganic particles to the binder polymer satisfies the above range, it is possible to prevent the problem that the pore size and the porosity of the coating layer formed by increasing the content of the binder polymer decrease, and the binder height can be prevented. It is also possible to solve the problem that the peeling resistance of the coating layer formed by reducing the molecular content is weakened.

In the porous coating layer, a large number of inorganic particles are filled and bound to each other by the binder polymer in a state of being in contact with each other, whereby an interstitial volume is formed between the inorganic particles. , The interstitial volume between the inorganic particles becomes an empty space and forms pores.

That is, the binder polymer adheres to each other so that the inorganic particles can be maintained in a state of being bound to each other, for example, the binder polymer connects and fixes the inorganic particles to each other. Further, the pores of the porous coating layer are pores formed by forming an interstitial volume between the inorganic particles, which is a closed packed or dense packed structure. It is a space limited by the inorganic particles that are substantially in contact with each other.

The inorganic particles are selected from the group consisting of inorganic particles having a dielectric constant of about 5 or more, inorganic particles having a lithium ion transfer ability, and a mixture thereof.

According to one embodiment of the present invention, the electrolytic solution contains a salt having a structure such as A ⁺ B ⁻ . Here, A ⁺ includes an alkali metal cation such as Li ⁺ , Na ⁺ , K ⁺ or an ion composed of a combination thereof, preferably a Li ⁺ ion. B ^- is F-, ^{Cl- ,} Br- ^, I- ^, NO _3- ^, BF _4- ^, PF _6- ^, N (CN) _2- ^, SCN, ClO _4- ^, AsF _6- ^, CF ₃ SO _3- ^, (CF ₃ SO ₂ ) _2- ^, C (CF ₂ SO ₂ ) _3- ^, (CF ₃ ) ₃ PF _3- ^, (CF ₃ ) ₄ PF _2- ^, (CF ₃ ) ₅ PF- ^, (CF ₃ ) ₆ P- ^, (CF ₃ CF ₂ SO _2- ⁾ ₂ N, (CF ₃ SO ₂ ) ₂ N- ^, CF ₃ SO _3- ^, CF ₃ CF ₂ (CF ₃ ) ₂ CO- ^, (CF ₃ SO ₂ ) ₂ Includes anions such as CH- ^, ₍ CF ₃ SO ₂ ) ₃ C- ^, CF ₃ (CF ₂ ) ₇ SO _3- ^, CF ₃ CO ^{2- ,} CH ₃ CO _2- or a combination thereof. Desirably, the salt having such an A ⁺ B ^- structure is a lithium salt.

Salts of such A ⁺ B ^- structure are dissolved or dissociated in organic solvents. Examples of organic solvents include, but are not limited to, propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), dimethyl sulfoxide, acetonitrile, dimethoxyethane, etc. Diethoxyethane, tetrahydrofuran, N-methyl-2-pyrrolidone (NMP), ethylmethyl carbonate (EMC), γ-butyrolactone) or mixtures thereof can be mentioned.

The electrolytic solution can be injected at an appropriate stage in the battery manufacturing process depending on the manufacturing process of the final product and the required physical characteristics. That is, it can be applied before assembling the battery or at the final stage of battery assembly.

According to one aspect of the present invention, there is provided a battery module containing the lithium secondary battery as a unit battery and a battery pack containing the battery module.

As described above, the lithium secondary battery of the present invention uses lithium titanium oxide as a negative electrode active material so that improvement in output characteristics can be achieved without substantially reducing high temperature characteristics and battery capacity. By using an inexpensive lithium manganese composite oxide having high room temperature stability as a positive electrode active material, it is possible to provide a battery pack that can be used more efficiently as a substitute for a lead storage battery of an automobile or for additional mounting.

The battery pack is in the form of a plurality of lithium secondary batteries connected in series, or a plurality of lithium secondary battery modules embodied by connecting a plurality of lithium secondary batteries in parallel are connected in series. Can be in the form of

The battery pack can be used as a power source for devices that require high temperature stability, long cycle characteristics, high rate characteristics, and the like. Specific examples of the device include a power tool powered by an electric motor; an electric vehicle (EV), a microhybrid electric vehicle (μ-HEV), and a hybrid electric vehicle (HEV). ), Vehicles including Plug-in Hybrid Electric Vehicles, PHEVs, etc .; Two-wheeled vehicles including E-bikes, E-scooters; electric golf carts Examples include, but are not limited to, power storage systems.

Hereinafter, the present invention will be described with reference to specific examples. However, the examples according to the invention can be transformed into many other embodiments and should not be construed as limiting the scope of the invention to the examples described below. The embodiments of the present invention are provided to more fully explain the present invention to those with average knowledge in the art.

[Example 1]
As shown in Table 1 below, a negative electrode was produced using lithium-titanium oxide Li ₄ Ti ₅ O ₁₂ powder in which the particle morphology, specific surface area, average particle size (D50) and pellet density were changed.

92% by weight of the lithium titanium oxide Li ₄ Ti ₅ O ₁₂ powder, 4% by weight of carbon black as a conductive material, 4% by weight of polyvinylidene fluoride (PVdF) as a binder, and N-methyl-2-pyrrolidone (NMP) as a solvent. ) To produce a negative mixture slurry. The produced negative electrode mixture slurry is applied to an aluminum (Al) thin film which is a negative electrode current collector having a thickness of about 20 μm, dried, and then rolled pressed to form an active material layer having a porosity of about 33%. Manufactured the negative electrode.

<Manufacturing of positive electrode>
Li (Ni _0.4 Co _0.3 Mn _0.3 ) O ₂ 91% by weight as the positive electrode active material, 3.5% by weight of carbon black as the conductive material, 5.5% by weight of polyvinylidene fluoride as the binder, in a solvent. A positive electrode mixture slurry was prepared by adding to a certain N-methyl-2-pyrrolidone. The positive electrode mixture slurry was applied to an aluminum (Al) thin film which is a positive electrode current collector having a thickness of about 20 μm, dried, and then rolled pressed to produce a positive electrode.

<Manufacturing of lithium secondary batteries>
An electrode assembly is manufactured by interposing a porous polyethylene separator between the positive electrode and the negative electrode manufactured in this manner, and then the electrode assembly is housed in a pouch-type battery case to form ethylene carbonate (EC) and diethyl carbonate (DEC). A lithium secondary battery was manufactured by injecting and sealing an electrolyte in which 1M LiPF ₆ was dissolved in a solvent in which and was mixed at a volume ratio of 30:70.

<Manufacturing of half cell>
A half cell was manufactured as follows.

92% by weight of the lithium titanium oxide Li ₄ Ti ₅ O ₁₂ powder, 4% by weight of carbon black as a conductive material, and 4% by weight of polyvinylidene fluoride as a binder are added to the solvent N-methyl-2-pyrrolidone to cause a negative electrode. A mixture slurry was produced. The slurry was applied onto aluminum foil to a thickness of 90 μm and then vacuum dried at 120 ° C. to produce a negative electrode (loading amount: 145 ± 5 mg / 25 cm ² ).

Then, after making the negative electrode into a circle with a diameter of 12 mm, a 2032 type coin half cell was manufactured by using a lithium metal foil as a relative electrode. At this time, as the electrolytic solution, a 1.0 M LiPF ₆ solution dissolved in a solvent in which ethyl methyl carbonate, propylene carbonate and dimethyl carbonate were mixed at a volume ratio of 2: 2: 6 was used.

[Examples 2 to 6]
The same method as in Example 1 except that lithium-titanium oxide Li ₄ Ti ₅ O ₁₂ powder with varying particle morphology, specific surface area, average particle size (D50) and pellet density was used as shown in Table 1 below. Negatives, lithium secondary batteries and half cells were manufactured respectively.

[Comparative Examples 1 to 8]
The same method as in Example 1 except that lithium-titanium oxide Li ₄ Ti ₅ O ₁₂ powder with varying particle morphology, specific surface area, average particle size (D50) and pellet density was used as shown in Table 1 below. Negatives, lithium secondary batteries and half cells were manufactured respectively.

[Measurement of characteristics]
(1) Specific Surface Area The specific surface area of the lithium titanium oxide Li ₄ Ti ₅ O ₁₂ powder used in Examples 1 to 6 and Comparative Examples 1 to 8 was measured as follows.

After heat-treating the Li ₄ Ti ₅ O ₁₂ powder at 200 ° C., the specific surface area was measured using a BET specific surface area analyzer (Brunauer Emmet Teller, BET). The results are shown in Tables 1 and 3.

(2) Average particle size (D50)
The average particle size of the lithium titanium oxide Li ₄ Ti ₅ O ₁₂ powder used in Examples 1 to 6 and Comparative Examples 1 to 8 was measured as follows.

To a 10 ml vial, add 0.35 g of Li ₄ Ti ₅ O ₁₂ powder and 5 drops of NaPO ₃ 10 wt% solution as a dispersant, pour water into the vial and perform ultrasonic decomposition treatment (sonification) 2 After applying for a minute, the treated powder was measured for average particle size using a particle size analyzer (manufactured by Microtrac). The results are shown in Tables 1 and 3.

(3) Pellet Density The rolling density of the lithium titanium oxide used in Examples 1 to 6 and Comparative Examples 1 to 8 was measured using a powder resistance measuring machine MCP-PD51 manufactured by Mitsubishi Chemical Corporation. The results are shown in Tables 1 and 3.

(4) Li insertion reference initial capacity (0.2C, mAh / g)
Using the half cells produced in Examples 1 to 6, Comparative Examples 1 to 4 and Comparative Examples 6 to 8, measurements were made at 0.2 C based on the second discharge (Li insertion) capacity. The cutoff voltage was 1.0V to 2.5V.

(5) Rate (insertion standard) capacity ratio (10C / 0.2C) (%)
Using the half cells manufactured in Examples 1 to 6, Comparative Examples 1 to 4 and Comparative Examples 6 to 8, charging and discharging are performed according to the pattern shown in Table 2 below, and the discharge capacity is 3 with respect to the ^0.2C discharge capacity of the second cycle of the 1st stage. The ratio of the 10C discharge capacity in the ^rd stage was measured. At this time, a rest period of 20 minutes was given between each stage. The measurement results are shown in Table 3.

The larger the value of this capacity ratio, the better the diffusion to lithium in the battery, which means that the electrolytic solution sufficiently impregnates the LTO active material particles (wetting), which is advantageous for forming a high output battery. ..

Referring to Table 3, in the case of Examples 1 to 6 of the present invention, the average particle size (D50) of 0.5 μm to 9 μm, the specific surface area of 3 m ² / g to 7 m ² / g, and the pressure of 64 MPa. As a result of applying lithium titanium oxide particles satisfying all pellet densities of 1.7 g / cc or more as the negative electrode active material, it can be confirmed that the capacity and rate characteristics of the battery are both excellent and applicable to a high output battery. ..

On the other hand, in the comparative example, since one or more of the average particle size, the specific surface area, and the pellet density are not satisfied, the capacity rate characteristics are inferior, the electrode is difficult to manufacture, or the cell design itself is impossible. there were.

Claims (4)

A negative electrode active material containing lithium-titanium oxide particles,
The lithium titanium oxide particles are all primary particles, having an average particle size (D50) of 0.5 μm to 1.2 μm, a specific surface area of 5 m ² / g to 7 m ² / g, and a pressure of 64 MPa. With a pellet density of 1.7 g / cc to 1.82 g / cc .
The negative electrode active material in which the lithium titanium oxide is represented by the following chemical formula 1:
[Chemical 1]
Li _{x Ty Oz M w}
(In the formula, M is one or a mixture of two or more selected from the group consisting of Zr, B, Sn, S, Be, Ge and Zn, 0.5 ≦ x ≦ 5, 1 ≦ y ≦ 5. , 2 ≦ z ≦ 12, 0 ≦ w <0.1). The lithium titanium oxide is Li _0.8 Ti _2.2 O ₄ , Li _2.67 Ti _1.33 O ₄ , Li _1.33 Ti _1.67 O ₄ , Li _1.14 Ti _1.71 O ₄ . The negative electrode active material according to claim 1, wherein the negative electrode active material is at least one selected from the group consisting of Li ₄ Ti ₅ O ₁₂ , Li Ti ₂ O ₄ and Li ₂ TiO ₃ . Metals (Me) in which the negative electrode active material is a carbonaceous material; Si, Sn, Li, Zn, Mg, Cd, Ce, Ni or Fe; alloys of the metals (Me); the metals (Me). 1), which further comprises any one active material selected from the group consisting of an oxide (MeOx); and a complex of the metal (Me) and carbon, or a mixture of two or more thereof. The negative electrode active material described in. A positive electrode containing a positive electrode active material, a negative electrode containing a negative electrode active material, a separator interposed between the positive electrode and the negative electrode, and an electrolytic solution are included.
A lithium secondary battery in which the negative electrode active material is the negative electrode active material according to any one of claims 1 to 3 .